At which Instant a double-barrel Gun is to be fired: the exact Time noted below: and the Time of hearing the Sound noted above.
These Notes are to be compared at the Aironaut’s arrival on Earth.
300. For such nice Experiments the Aironaut shoud ascend half an Hour before sunrise, or Sunset: and the Day chosen by the foregoing Rules.
The Air must be quite calm: but it is not necessary that it shoud be free from Clouds or Mist.
When the Rope is at its full Extent, the Operator below is to shorten it, by winding down the Balloon, 100 Yards: the Signals below, being repeated, till the Balloon is arrived within 100 Yards of the Ground.
To estimate the Densities at different Heights.
301. While one Observer below is writing down the Observation to be made the Instant the Balloon has risen exactly 100 Yards; another Operator is to weigh, by Hand, with Spring Steel-Yards, the Force of Levity already acquired, which is to be noted down by a third Bystander.
This Process is to be repeated at every 100 Yards.
The Levity, it is true, will encrease as the Balloon rises, (probably in a geometric Progression;)[100] yet the Cord, by rising with the Balloon, will greatly check it: if, however, it prove insufficient for that Purpose, and, lest the Cord shoud be in Danger of breaking; the Bottom of the Balloon must be opened, or the upper Valve drawn.
If the Cord, Rope, or Balancer, be sufficiently strong; there will be no Necessity for the Aironaut to throw out Ballast occasionally; nor for the Observations in the former Part of this Section: the Densities will likewise be more easily determined, by the Weights; which shew the Encrease of Levity and Expansion of the Balloon, at each of the given Heights: Allowance being made for the Weight of the Balance Rope, raised by the Balloon.